Enhancing gas-phase reaction in a plasma using high intensity and high power ultrasonic acoustic waves

ABSTRACT

This invention relates to enhancing a gas-phase reaction in a plasma comprising: creating plasma by at least one plasma source, and wherein that the method further comprises: generating ultrasonic high intensity and high power acoustic waves having a predetermined amount of acoustic energy by at least one ultrasonic high intensity and high power gas-jet acoustic wave generator, where said ultrasonic high intensity and high power acoustic waves are directed to propagate towards said plasma so that at least a part of said predetermined amount of acoustic energy is absorbed into said plasma, and where a sound pressure level of said generated ultrasonic high intensity and high power acoustic waves is at least substantially 140 dB and where an acoustic power of said generated ultrasonic high intensity and high power acoustic waves is at least substantially 100 W.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.12/599,782, filed May 13, 2008, which is the National Stage ofInternational Patent Application No. PCT/EP2008/055801, filed May 13,2008, which claims priority to Denmark Patent Application No. PA 200700717, filed May 11, 2007, the disclosures of which are eachincorporated herein by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method of enhancing gas-phase reaction in aplasma. The invention further relates to a system for enhanced gas-phasereaction in a plasma.

BACKGROUND OF THE DISCLOSURE

A plasma is an ionized gas. Active species of ions, electrons,high-energy neutrals, radicals as well as ultra-violet emission inplasmas can be used for various things. Plasma generation or a generatedplasma may also advantageously be utilized for various purposes orapplications like ozone generation, hydrogen production, exhaust gascleaning, pollution control, odor removal, fuel conversion,sterilization, oxidation, etc.

Ozone can be formed by recombination in triplets of single oxygen atomswhich are split from the diatomic oxygen in a plasma. Fuel conversion isthe chemical or physical transformation of a naturally occurring oralready modified fuel to improve the quality of the fuel. A fuelconversion process may result in one or more upgraded fuel productswhich may be solid, liquid, or gaseous, and may generate chemicals orraw materials for chemical manufacture. For example, coal generallyrequires size reduction, washing, and removal of inert species. Naturalgas may need removal of H₂S and CO₂ with separation of gas liquids andC2 compounds. However, “gas-to-liquid” fuel conversion (liquefaction) isalso of significant importance. Here CH₄, which is the major componentof natural gas, is converted to liquid fuels in one or more than onestep chemical reactions.

A variety of plasmas exists, including direct current plasmas,capacitively coupled plasmas, pulsed plasmas, magnetron plasmas,electron cyclotron resonance plasmas, inductively coupled plasmas,helicon plasmas, helical resonator plasmas, microwave plasmas, andplasma jets (see e.g. A Bogaerts et al. Spectrochimica Pt.B 57 (2002)609-658.). Many of them are operated at low pressures, suffering fromthe drawbacks that they require expensive vacuum systems. Furthermore,methods are only well-developed for batch or semi-batch treatments. Toovercome these drawbacks an atmospheric pressure plasma surfacemodification system can be used that not only avoids the need for vacuumequipment but also permits both the surface modification of largeobjects and production line continuous surface modification (see e.g. CTendero et al. Spectrochimica Pt.B 61 (2006) 2-30.).

A prior art plasma application system is shown in FIG. 1 and isexplained in more detail in the following. FIG. 1 illustrates an exampleof capacitively coupled plasma of the well-known so-called dielectricbarrier discharge (DBD) type usable at atmospheric pressure.

Other types or variations of plasma sources include dielectric barrierdischarges (DBDs) with a single dielectric barrier located substantiallyin the middle between the two electrodes or with a single dielectricbarrier covering only one of the electrodes. Such plasma sources aretypically also referred to as volume discharge (VD) sources where amicro-discharge can take place in thin channels generally randomlydistributed over the electrode- and/or dielectric-surface. Other DBDplasma sources include so-called surface discharge (SD) plasma sourcestypically comprising a number of surface electrodes on a dielectriclayer and a counter-electrode on the reverse side of the dielectriclayer. Such SD plasma sources may include a so-called SPCP(Surface-discharge-induced Plasma Chemical Processing) discharge elementor CDSD (Coplanar Diffuse Surface Discharge) element. In a SPCP,electrodes are attached on the dielectric(s) and in a CDSD theelectrodes are embedded in the dielectric(s).

Other types of plasma sources are e.g. so-called plasma torches such asarc plasma torches, cold plasma torches (see e.g. H Mortensen et al.Jpn. J Appl. Phys. 45(10B) (2006) 8506-8511.), atmospheric pressureplasma jet (APPJ), pencil like torches, barrier torches, and microwavetorches (see e.g. C Tendero et al. Spectrochimica Pt.B 61 (2006) 2-30.).Yet another type of plasma source is the so-called gliding arc (see forexample A Fridman et al. J. Phys. D Appl. Phys. 38 (2005) R1-R24).

Additional types of plasma sources are low pressure plasmas, coronadischarge (see e.g. A Bogaerts et al. Spectrochimica Pt.B 57 (2002)609-658) and microplasmas (see e.g. V Karanassios Specrochimica ActaPt.B 59 (2003) 909-928). See e.g. A Bogaerts et al. Spectrochimica Pt.B57 (2002) 609-658, U Kogelschatz Plasma Chem. Plasma Proc. 23(1) (2003)1-46, C Tendero et al. Spectrochimica Pt.B 61 (2006) 2-30 and A Fridmanet al. J. Phys. D Appl. Phys. 38 (2005) R1-R24) for further details ofplasmas and atmospheric pressure plasmas.

The three articles ‘Ozone generation by hollow-needle to plateelectrical in an ultrasound field’, J. Phys. D: Appl. Phys. 37 (2004)1214-1220, ‘Ultrasound and airflow induced thermal instabilitysuppression of DC corona discharge: an experimental study’, PlasmaSources Sci. Technol. 15 (2006) 52-58, and ‘Ultrasonic resonator withelectrical discharge cell for ozone generation’, Ultrasonics 46 (2007)227-234, by Stanislav Pekárek, Rudolf Bálek et al. disclose suppressionof DC corona discharge where ultrasound or ultrasound combined with anairflow is used in connection with a hollow needle-to-plate electrodesystem to activate the corona discharge for ozone production. It wasalso found that the application of ultrasound waves increases ozonegeneration.

The article ‘Improvement of Charging Performance of Corona Charger inElectrophotography by Irradiating Ultrasonic Wave to Surrounding Regionof Corona Electrode’ (Kwang-Seok Choi, Satoshi Nakamura and Yuji MurataJpn. J. Appl. Phys. 44(5A) (2005) 3248-3252.) discloses improvement ofthe charging speed of a corona charger in electrophotography using anultrasonic wave where the ultrasonic wave increases the charge densityon an insulator layer of a coated aluminum drum used instead of aphotoreceptor drum used for printing. At least some of the findings inthe articles have also been disclosed in patent application CZ 295687.

The ultrasonic generators disclosed in the above-mentioned articles arebased on piezoelectric transducers. No mention is given of specific orpreferred sound pressure levels of the emitted acoustic waves orultrasonic waves or the advantages thereof.

Furthermore, the articles mention that the acoustic pressures developedby ultrasonic layouts are, respectively, of the order of 2 and 10 kPanear the emitting surface of the transducer at the frequency ofgenerated ultrasound of 20.3 kHz. In the fourth article, the ultrasonicgenerator is a 28-kHz 50-mm-diam and 80-mm-height bolt-clampedLangevin-type piezoelectric transducer. The maximum input power is 50 W.These values give an estimation of the emitted acoustic pressure valueto be approximately 2 kPa. The pressure values of 2 and 10 kPacorrespond to very high sound pressure levels of 160 and 174 dB abovethe reference pressure of 20 μPa. It can be estimated that theabove-specified acoustic pressures at the above frequency correspond toultrasound intensities of 4.4 and 20 kW/m² or the sound intensity levelsof 156 and 163 dB above the reference intensity of 1 pW/m². Thischaracterizes the ultrasonic acoustic waves being applied in at leastsome of these articles as high-intensity. However, the acoustic powerprovided according to the articles is in fact too low and too localizedto allow for efficient and high-volume enhancement of the gas-phase in aplasma.

A similar situation can be outlined regarding the patent specificationU.S. Pat. No. 6,391,118. It discloses a method for removing particlesfrom the surface of an article in an apparatus using corona discharge.The particles are supplied with an electric charge and subsequently anultrasonic wave or gas stream is applied onto the surface of the articlewhile an electric field is applied for driving away the electricallycharged solid particles from the surface. The application of anultrasonic wave and/or gas further facilitate the removal of theelectrically charged solid particles. The variety of ultrasonicgenerators (oscillators) here includes a piezoelectric oscillator, apolymer piezoelectric membrane, an electrostrictive oscillator, aLangevin oscillator (that is as mentioned above just a special type ofpiezoelectric transducers), a magnetostrictive oscillator, anelectrodynamic transformer, and a capacitor transformer. Use of suchoscillators provides acoustic power that is low (no more than 50 W) andlocalized. It is too low and localized to allow for efficient andhigh-volume enhancement of the gas-phase in a plasma. Moreover, nodisclosure is given of a specific or preferred sound pressure level ofthe emitted ultrasonic waves or the advantages thereof.

The article ‘Current Waveforms of Electric Discharge in Air underHigh-Intensity Acoustic Standing Wave Field’, Japanese Journal ofApplied Physics, Vol. 43, No. 5B, 2004, pp. 2852-2856, Nakane et al.also discloses an electric discharge phenomenon in a high-intensityacoustic field. Here standing waves with a frequency of 660 Hz are used,which limits a discharge volume for ozone production. The enhanced ozoneproduction according to this article can be explained by Paschen's lawsignifying that the lower the static pressure, the higher the growthrate of the discharge streamers. Therefore, the streamers should growmore intensively in the nodes of standing waves. Another part of theproposed mechanism is that streamer channels oscillate in the acousticfield.

Patent application US 2003/0165636 discloses a process for atmosphericpressure plasma surface modification of an object's surface whereexcitation of the surface to be treated is done so that it vibrates andundulates thereby activating the application of plasma. The energy forexcitation of the surface may come from the process of creating theplasma, from an external source, or from a combination thereof. Theenergy for excitation of the surface may come from a vibration generatorbrought in contact with the object to be treated or by indirect contactfrom a vibration generator emitting acoustic waves, e.g. ultrasonicwaves, to the object to be treated so that it provokes turbulent plasma.No disclosure is given of a specific or preferred sound pressure levelof the acoustic waves or the ultrasonic waves or the advantages thereof.Therefore, exciting surface vibrations and undulations, or in otherwords, generation of guided and surface acoustic waves on the object issuggested in order to intensify a plasma treatment. Correspondingly, itis disclosed that the vibration of the surface to be treated can be theresult of excitation at one or several eigenfrequencies and theirharmonics associated with the body of the object to be treated. Thus,either the range of the characteristic dimension of the modified object(primarily its thickness) is strictly limited by the operating frequencyof the used source of acoustic energy, or the said frequency is strictlydetermined by the dimension of the object. It is also disclosed that thevibration of the surface can also result from forced frequencies when anexternal generator of acoustic waves emits frequencies that are notharmonics of the eigenfrequencies of the object to be treated. Thissignifies generation of surface acoustic waves (primarily the Rayleighsurface waves).

The following procedures of transfer of acoustic power into ambientgas/plasma are mentioned.

-   -   1. External acoustic generator→Treated object surface        vibration→Gas molecules (plasma particles) vibration.    -   2. Generation of the treated surface object vibration directly,        for instance through a direct acoustic contact→Gas molecules        (plasma particles) vibration.

Both procedures require acoustic waves to overpass the solid/gasinterface at least once. However, due to more thanfour-orders-of-magnitude difference in acoustic impedance for a solidand a gas, most of generated acoustic power cannot be emitted (andespecially re-emitted) into the gas atmosphere and remains in a solidbeing ultimately converted into thermal energy. Thus, it is not possiblein this way to generate sound or ultrasound in the air with a power thatwould be enough to enable efficient and high-volume enhancement of agas-phase in a plasma. Therefore, it is of prime importance not simplyto “shake” the surface up and provoke uncontrolled turbulent plasma withunknown efficiency and spatial distribution in such a way, but rather toenable efficient and high-volume enhancement of the gas-phase in aplasma.

The generated acoustic power is relatively low (at any rate, below 100W) because the power applied to the acoustic wave transmitter isactually 100 W, and the efficiency of sound generation in a gasatmosphere cannot exceed ˜30% even for the most effective gas-jetultrasonic transmitters, not to mention other methods.

A principal impediment to the generation of a plasma or other plasmaprocesses are how to enable a very efficient gas-phase reaction overlarge volumes in a plasma.

None of the mentioned prior art disclosures specify an acoustic powerlevel sufficient to efficiently allow for efficient and high-volumeenhancement of the gas-phase in a plasma.

Furthermore, the prior art involving piezoelectric transducers or othertransducers involving a solid to transfer the energy, only provides theenergy in a very localized fashion, e.g. very close to the piezoelectrictransducer (or other solid transducer) and is therefore not suitable forhigh volume gas-phase enhancement.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of and a system forenhanced gas-phase reaction in a plasma that alleviates theabove-mentioned shortcomings of prior art at least to an extent.

It is another object to enable enhancement of a plasma gas-phasereaction in a large volume.

An additional object is to speed a plasma process up.

A further object of some embodiments is to enhance a generation processinvolving a plasma—e.g. hydrogen, ozone or syngas generation usingplasma, exhaust gas cleaning, pollution control, odor removal, fuelconversion, liquefaction, sterilization, oxidation, etc. using a plasma.

These objectives are obtained at least to an extent by a method ofenhancing a gas-phase reaction in a plasma comprising: creating plasmaby at least one plasma source, and wherein that the method furthercomprises: generating ultrasonic high intensity and high power acousticwaves having a predetermined amount of acoustic energy by at least oneultrasonic high intensity and high power gas-jet acoustic wavegenerator, where said ultrasonic high intensity and high power acousticwaves are directed to propagate towards said plasma so that at least apart of said predetermined amount of acoustic energy is absorbed intosaid plasma, and where a sound pressure level of said generatedultrasonic high intensity and high power acoustic waves is at leastsubstantially 140 dB and where an acoustic power of said generatedultrasonic high intensity and high power acoustic waves is at leastsubstantially 100 W.

In this way, a high sound intensity and power are obtained thatefficiently enhances a gas-phase reaction in the plasma, which enhancesthe plasma process, e.g. enabling more efficient ozone or syngasgeneration using plasma, exhaust gas cleaning, pollution control, odorremoval, fuel conversion, liquefaction, sterilization, oxidation, etcusing a plasma in relation to reaction speed and/or obtainedconcentration of the generated compound.

Increasing the concentration of aimed products, reducing theconcentration of pollutants, odor etc. and/or reducing the reactiontime, reduces the cost of the process since the process is expensive andrequires a lot of energy.

As a comparison, the sound-emitting surface area of transducers, e.g.like the ones described in the previous mentioned prior art articles(‘Ozone generation by hollow-needle to plate electrical in an ultrasoundfield’; ‘Ultrasound and airflow induced thermal instability suppressionof DC corona discharge: an experimental study’; and ‘Improvement ofCharging Performance of Corona Charger in Electrophotography byIrradiating Ultrasonic Wave to Surrounding Region of Corona Electrode’)is of the order of 2×10⁻³ m² and the emitted acoustic power is 10-40 W.

The acoustic power provided by a high-power gas-jet generator is capableof much higher acoustic power outputs along with the high sound pressureand intensity levels of 140 or 150 to 170 dB (see e.g. Y. Y. Borisov,Acoustic gas-jet generators of Hartmann type, in L. D. Rozenberg (ed.)Sources of High-Intensity Ultrasound (New York: Plenum: 1969) part I.and Levavasseur, R. High power generators of sound and ultrasound. USPatent, book 116-137, No. 2755767 (1956).).

It has been shown that an acoustic power of about 100 W or more enhancesthe gas-phase reaction in a plasma.

A high-power gas-jet generator is normally capable of an acoustic powerof several hundreds watts (i.e. approximately one order of magnitudehigher than the piezoelectric transducer acoustic power output) andtypical SPL (sound pressure level) of 160 dB at 10 cm from the generatororifice at the frequency of 20-30 kHz. Even an acoustic power of 1-2 kWis attainable.

The main physical reason for such a dramatic difference in acousticpower outputs of piezoelectric (or other solid-state acoustictransducers) and gas-jet generators is that a piezoelectric transducerworks by vibrating (using sound) a solid being in contact with a gas andthus transfers the vibrations to the gas. Due to the tremendousdifference in acoustic impedance for a solid and a gas (a so-calledacoustic impedance mismatch), most of generated acoustic power cannot beemitted in the ambient gas and remains in a solid. It is converted intothermal energy and results in a transducer warming-up.

Consequently, it is not possible in this way to generate sound orultrasound in the gas with a power that would be enough to enhance agas-phase reaction in a plasma sufficiently. In fact, a singlepiezoelectric transducer provides the high-intensity ultrasoundradiation only nearby its emitting surface and irradiates a limitedsurface area that is comparable with the area of its emitting surface.That is because of the acoustic wave diffraction, which is significantwhen the transducer diameter is comparable with the acoustic wavelength.Indeed, for ultrasound frequency of 20-30 kHz in the air the wavelengthis about 10-20 mm that is of the order of the actual transducerdiameter. In the case of gas-jet ultrasonic transmitters, a vibratingmedia is not a solid but a gas. It is clear that there is no anyimpedance mismatch and high enough acoustic power can be emitted in theambient gas. Moreover, intensity and sound pressure levels of ultrasoundradiation remain very high at several tens of centimeters from thegas-jet transmitter orifice while the acoustic wave front is broad (itis sometimes just a spherical wave front). In this way, it is possibleto expose large volumes to high-intensity ultrasound (sound intensityand sound pressure levels of substantially 140 dB and above atapproximately 10 cm from the generator's orifice) and enable anefficient gas-phase reaction in a plasma.

In one embodiment, the acoustic pressure level of said generatedultrasonic high intensity and high power acoustic waves is

-   -   at least substantially 150 dB,    -   at least substantially 160 dB,    -   at least substantially 170 dB,    -   at least substantially 180 dB,    -   at least substantially 190 dB, or    -   at least substantially 200 dB.

where the sound pressure level as they are at 10 cm from the generatororifice.

In one embodiment, the acoustic power of said generated ultrasonic highintensity and high power acoustic waves is

-   -   at least substantially 200 W,    -   at least substantially 300 W,    -   at least substantially 400 W,    -   about 400 W,    -   greater than substantially 400 W,    -   at least substantially 500 W,    -   at least substantially 1 kW, or    -   selected from about 1-2 kW.

It is to be understood, that if several acoustic generators are usedeven higher powers may be obtained.

In one embodiment, the plasma source comprises at least one sourceselected from a group of: a dielectric barrier discharge (DBD) plasmasource, a surface discharge (SD) plasma source, a volume discharge (VD)plasma source, a plasma torch source, an arc plasma torch, a gliding arcplasma torch, a cold plasma torch, a pencil-like torch, a direct currentplasma source, a capacitively coupled plasma source, a pulsed plasmasource, a magnetron plasma source, an electron cyclotron resonanceplasma source, an inductively coupled plasma source, a helicon plasmasource, a helical resonator plasma source, a microwave plasma source, anatmospheric pressure plasma jet (APPJ) source, a barrier torch, an arcmicrowave torch, a corona discharge plasma source, a micro-plasmasource, a low pressure plasma source, and a high pressure plasma source.

In one embodiment, a working gas pressure at an inlet of the at leastone ultrasonic high intensity and high power gas-jet acoustic wavegenerator is between approximately 1.9 and approximately 5 bar.

In one embodiment, the plasma is created at atmospheric pressure.

In one embodiment, the plasma source comprises at least one electrodeand wherein one electrode of said at least one electrode is a mesh typeof electrode.

This allows the gas/energy to pass through the ‘upper’ electrode in avery simple and efficient way.

In one embodiment, the generated ultrasonic high intensity and highpower acoustic waves are propagated towards a membrane so that any gasesused by the at least one ultrasonic high intensity and high poweracoustic wave generator is not mixed with one or more gases used by saidplasma source to create said plasma.

In one embodiment, the generated ultrasonic high intensity and highpower acoustic waves are generated using a gaseous medium and where theacoustic waves are directed towards said plasma and wherein said gaseousmedium after exit of said at least one ultrasonic high intensity andhigh power gas-jet acoustic wave generator is directed away from saidplasma.

In one embodiment, the generated ultrasonic high intensity and highpower acoustic waves do not spatially overlap with the working gas flowoutgoing from the generator orifice. Moreover, since the generatedultrasonic high intensity and high power acoustic waves are directedtoward the plasma and the gas outgoing from the ultrasonic highintensity and high power acoustic wave generator do not overlap inspace, the said outgoing working gas is not mixed with one or more gasesused by said plasma source to create said plasma.

In these ways, control of the gas environment for the plasma generationprocess is enabled.

In one embodiment, a gas mixture, which is used for creating the plasma,is supplied to at least one electrode of the plasma source substantiallyin a direction that said ultrasonic acoustic waves propagate towardssaid plasma.

In one embodiment, at least one of the ultrasonic high intensity andhigh power gas-jet acoustic wave generators are selected from the groupof:

-   -   a Hartmann type gas-jet generator,    -   a Levavasseur type gas-jet generator,    -   a generator comprising an outer part and an inner part defining        a passage, an opening, and a cavity provided in the inner part,        where said ultrasonic high intensity and high power gas-jet        acoustic wave generator is adapted to receive a pressurized gas        and pass the pressurized gas to said opening, from which the        pressurized gas is discharged in a jet towards the cavity,    -   a generator of any of the above mentioned types, which includes        any type of concentrators or reflectors of acoustic waves

In one embodiment, a food item is subjected to the plasma where thecreation of the plasma generates chemical radicals and sterilizes thefood item.

In one embodiment, the generating ultrasonic high intensity and highpower acoustic waves comprises:

-   -   generating high intensity and high power acoustic waves by a        first acoustic wave generator using a gaseous medium where the        gaseous medium, after exit from the first acoustic wave        generator, has a first principal direction that is different        from a second principal direction of the high intensity and high        power acoustic waves generated by the first acoustic wave        generator,    -   generating high intensity and high power acoustic waves by a        second acoustic wave generator,    -   where the first and second acoustic wave generators are located        in relation to each other so that at least a part of the        generated high intensity acoustic waves, being generated by said        second acoustic wave generator, is directed towards at least a        part of the gaseous medium after exit from said first acoustic        wave generator.

In one embodiment, the plasma is used in a process selected from thegroup of:

-   -   ozone generation,    -   hydrogen production,    -   exhaust gas cleaning,    -   pollution control,    -   odor removal,    -   fuel conversion,    -   sterilization, and    -   oxidation.

The present invention also relates to a system corresponding to themethod of the present invention. More specifically, the inventionrelates to a system for enhancing a gas-phase reaction in a plasmacomprising: at least one plasma source adapted to create plasma, whereinthat the system further comprises: at least one ultrasonic highintensity and high power gas-jet acoustic wave generator adapted togenerate ultrasonic high intensity and high power acoustic waves havinga predetermined amount of acoustic energy and being directed topropagate towards said plasma so that at least a part of saidpredetermined amount of acoustic energy is absorbed into said plasma,and where a sound pressure level of said generated ultrasonic highintensity and high power acoustic waves is at least substantially 140 dBand where an acoustic power of said generated ultrasonic high intensityand high power acoustic waves is at least 100 W.

Advantageous embodiments of the system are defined in the sub-claims andare described in detail in the following. The embodiments of the systemcorrespond to the embodiments of the method and have the same advantagesfor the same reasons.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the illustrative embodiments shown in thedrawings, in which:

FIG. 1 schematically illustrates a prior art plasma apparatus;

FIG. 2 schematically illustrates a block diagram of a plasma apparatus;

FIG. 3a schematically illustrates a (turbulent) flow without applicationof ultrasonic high intensity and high power acoustic waves;

FIG. 3b schematically illustrates a flow where the effect of applyingultrasonic high intensity and high power acoustic waves to/in air/gas isillustrated;

FIG. 4 schematically illustrates one embodiment of an enhanced plasmaapparatus;

FIG. 5 schematically illustrates an alternative embodiment of anenhanced plasma apparatus;

FIG. 6 schematically illustrates an alternative embodiment of anenhanced plasma apparatus;

FIG. 7 schematically illustrates an embodiment of an enhanced plasmaapparatus where the plasma source is a surface discharge (SD) plasmasource;

FIG. 8 schematically illustrates an embodiment of an enhanced plasmaapparatus where the plasma source is a torch plasma source e.g. agliding arc plasma source:

FIG. 9 schematically illustrates an embodiment of a high intensity andhigh power gas-jet acoustic wave generator wherein a convergingsupersonic gas jet outgoing a ring-shaped nozzle and braking in amushroom resonator has the form of a disk (i.e. the so-called disk-jetHartmann ultrasound generator);

FIG. 10 is a sectional view along the diameter of the high intensity andhigh power acoustic wave generator (101) in FIG. 9 illustrating theshape of an opening (302), a gas passage (303) and a cavity (304) moreclearly;

FIG. 11 schematically illustrates another embodiment of a high intensityand high power acoustic generator in form of an elongated body; and

FIG. 12 schematically illustrates an embodiment of a high intensity andhigh power acoustic generator comprising two generators.

Throughout the figures, same reference numerals indicate similar orcorresponding features.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a prior art plasma reaction orgeneration apparatus. Shown is an example of a plasma generator orplasma source, i.e. any device or method capable of creating a plasma(forth only denoted plasma source) of the well-known so-calleddielectric barrier discharge (DBD) type usable even at atmosphericpressure. Shown are a number of gases (111), such as He, Ar, O₂, CO₂,and NH₃ supplied to a gas mixing unit (110) mixing the gases into aproper composition for the given use or application. The selected gasesfor the plasma should be selected based on the specific type of plasmareaction or compound generation process being used and may be any gas,which is ordinarily used for such processes. Specific and typicalexamples include air, natural gas, CH₄, He, Ar, Ne, Xe, air, N₂, O₂,H₂O, CO₂, halogen compound gases such as Freon gases (CF₄, CHF₃, C₃F₆,C₄F₈ etc.), halon gases, NH₃, NF₃, SF₆, organic compound gases (CH₄,C₂H₆, C₂H₄, C₂H₂, C₆H₆, C₂H₅OH, etc.), NOx (nitrogen oxides), SO₂,silanes etc. and gas mixtures selected from them. In order to stabilizethe plasma, the gas(es) can be diluted with He, Ar, see e.g. Europeanpatent EP 0508833 B1.

Further shown are two electrodes (103) placed apart with a discharge gapbetween them, where at least one of the electrodes (103) is adjoined orcovered with an insulating or dielectric material (105) on a side of theelectrode facing the other electrode in order to avoid arcing. In thefigure, both electrodes (103) are adjoined or covered with dielectricmaterial (105). One electrode (103) is connected to a suitable powersupply (114), being connected to ground and supplying AC high voltage,e.g. 0.1 kHz-500 kHz, between the electrodes (103).

Further, shown is a high voltage probe (113) connected to the powersupply (114) and an oscilloscope connected to the high voltage probe(113). The high voltage probe is used for monitoring the appliedvoltage, but is not relevant for and does not influence plasma process.

The gas mix is supplied from the gas-mixing unit (110) to the dischargearea between the two electrodes (103) and, as a result, plasma (104) iscreated when voltage is applied to the electrodes (103). A specimen orobject (not shown) may be located in the plasma (104) e.g. for surfacemodification, treatment, processing, etc.

The plasma process taking place may e.g. involve ozone generation,hydrogen production, syngas production, exhaust gas cleaning, pollutioncontrol, odor removal, fuel conversion, sterilization, oxidation, etc.

Ozone can be formed by recombination in triplets of single oxygen atomswhich are split from the diatomic oxygen in a plasma. Fuel conversion isthe chemical or physical transformation of a naturally occurring oralready modified fuel to improve the quality of the fuel. A fuelconversion process may result in one or more upgraded fuel productswhich may be solid, liquid, or gaseous, and may generate chemicals orraw materials for chemical manufacture. For example, coal generallyrequires size reduction, washing, and removal of inert species. Naturalgas may need removal of H2S and CO2 with separation of gas liquids andC2 compounds. However, “gas-to-liquid” fuel conversion (liquefaction) isalso of significant importance. Here CH₄, which is the major componentof natural gas, is converted to liquid fuels in one or more than onestep chemical reactions. One well-known process is first synthesize asyngas (CO+H₂);

CH₄+H₂O→CO+3H₂

CH₄+C₂O→2CO+2H₂

or

CH₄+O₂→CO+2H₂

and subsequently synthesize liquids;

CO+H₂→gasoline, diesel, alcohol, etc.

Plasma can also synthesize liquids (methanol, ethanol, benzene etc.) andother molecules (ethane, propane, ethylene, acetylene, propylene benzeneand heavier hydrocarbons) (K. V. Kozlov, P. Michel, H. E. Wagner“Synthesis of organic compounds from mixtures of methane with carbondioxide in dielectric barrier discharge at atmospheric pressure” Plasmasand Polymers, 5(3/4) (2000) 129-150, S. Kado, Y. Sekine, T. Nozaki, K.Okazaki “Diagnosis of atmospheric pressure low temperature plasma andapplication to high efficient methane conversion” Catalysis Today 89(2004) 47-55 etc.). Produced hydrogen gas can also be used for otherpurposes such as an environmentally friendly fuel for fuel cells.Petroleum refining and coal gasification are also examples. Examples ofquality upgrades are the manufacture of automotive gasoline by crackingof petroleum components, and removal of sulphur and nitrogen from liquidfuels by reacting the fuel with hydrogen.

Exhaust gas cleaning can be performed by passing through a plasma orinjecting activated species in to the exhaust. Its examples are NOx andSO₂ reduction.

Plasmas are useful for decomposing toxic gas components such as volatileorganic compounds (VOCs) (K. Urashima, J. S. Chang “Removal of volatilecompounds from air streams and industrial flue gases by non-thermalplasma technoklogy” IEEE Transactions on Dielectrics and ElectricalEngineering 7(5) (2000) 602-614) and odor such as NH3 (L. Xia, L. Huang,X. Shu, R. Zhang, W. Dong, H. Hou “Removal of ammonia from gas streamswith dielectric barrier discharge plasmas” 152 (2008) 113-119). They aregenerally decomposed by oxidation in a plasma.

A gas-phase reaction in the plasma (104) can be enhanced as shown andexplained in the following.

FIG. 2 schematically illustrates a block diagram of a plasmaprocess/apparatus. Illustrated are one or more plasma sources (106)creating or supplying plasma (104).

Further illustrated are one or more ultrasonic high intensity and highpower acoustic wave generators (101) generating high intensity and highpower ultrasound (102). According to the present invention, thegenerated ultrasound (102) is applied to at least a part of the plasma(104) whereby at least a part of the acoustic energy is absorbed by theplasma (104). The addition of energy to the plasma (104) will enhancethe gas-phase reaction and will enhance the plasma process taking place.The application of high intensity and high power ultrasonic acousticwaves with a sound pressure level of at least substantially 140 dB andan energy of at least substantially 100 W will enhance the gas-phasereaction and thereby the plasma process significantly, as explained inthe following in connection with FIGS. 3a and 3 b.

The working gas pressure at the inlet of the ultrasonic high intensityand high power acoustic wave generators (101) may be optimized so thathigh acoustic pressure can be generated. It is preferably between 1.9and 5 bar or between 2.5 to 4 bar and will typically depend on the typegenerator used. The gas pressure at the outlet of the high-power gas-jetgenerators is lower than that at the inlet, and can be practicallynearly equal to the gas pressure for the plasma process.

The air-pressure required for operation of gas-jet high-intensity andhigh-power ultrasonic generators is at least over 1.9 bar for operationunder normal conditions and the pressure required for optimal operationproviding stable generation of ultrasound with a SPL over 140 dB at 10cm from the generator orifice is 2.5 to 4 bar depending on a generatortype.

The one or more plasma sources (106) may be any plasma source suitablefor the given plasma process, e.g. such sources as explained earlier andin the following and/or combinations thereof or such sources e.g. usingone or more gases, as explained earlier, in creating the plasma. Theplasma source(s) (106) can be chosen among any existing ones (both lowand high pressure plasmas), and more specifically may be e.g. directcurrent plasmas, capacitively coupled plasmas, pulsed plasmas, magnetronplasmas, electron cyclotron resonance plasmas, inductively coupledplasmas, helicon plasmas, helical resonator plasmas, microwave plasmas,DBDs, SDs, plasma torches such as arc plasma torches, cold plasmatorches, APPJs, pencil like torches, barrier torches, arc plasmatorches, microwave torches, gliding arc, corona discharge, andmicroplasmas.

The gas pressure for the plasma process is preferably higher than 0.4bar and may be around atmospheric pressure or more, so that the acousticenergy can be delivered efficiently. One the other hand, it is easier togenerate plasmas at lower pressures. Therefore, the gas pressure for theplasma process is preferably more than 0.4 bar and less than thepressure at the inlet of the high-power gas-jet generators. Morepreferable plasma source may be DBDs, SDs, plasma torches such as arcplasma torches, cold plasma torches, APPJs, pencil like torches, barriertorches, microwave torches, gliding arc, corona discharge, andmicroplasmas, which can be operated at the pressures mentioned above.

The one or more ultrasonic high intensity and high power acoustic wavegenerator (101) is a gas-jet acoustic wave generator and may e.g. be oneor more Hartmann type gas-jet generators, one or more Levavasseur typegas-jet generators, etc. or combinations thereof and as explained in thefollowing and as shown in FIGS. 9-12.

The use of a gas-jet acoustic wave generator has advantages likedescribed earlier in terms of acoustic power, high intensity, acousticimpedance, etc.

If more than a single ultrasonic and high intensity and high poweracoustic wave generator is used they need not be of the same typealthough they can be.

The plasma process may e.g. be ozone generation, hydrogen production,exhaust gas cleaning, pollution control, fuel conversion, sterilization,oxidation, etc.

In one embodiment, a food item is subjected to the plasma process wherethe process will generate chemical radicals and sterilize the food itemin a very efficient way.

FIG. 3a schematically illustrates a (turbulent) flow without applicationof ultrasonic high intensity and high power acoustic waves.

Shown is a surface (314) of a solid object (100) where a gas or amixture of gases (500) surrounds or contacts the surface (314).

Thermal energy can be transported through gas by conduction as well asby the movement of the gas from one region to another. This process ofheat transfer associated with gas movement is usually referred to asconvection.

When the gas motion is caused only by buoyancy forces set up bytemperature differences, the process is normally referred to as naturalor free convection; but if the gas motion is caused by some othermechanism, it is usually referred to as forced convection. With acondition of forced convection, there will be a laminar boundary layer(311) near to the surface (314). The thickness of this layer is adecreasing function of the Reynolds number of the flow, so that at highflow velocities, the thickness of the laminar boundary layer (311) willdecrease. When the flow becomes turbulent the layer are divided into aturbulent boundary layer (312) and a laminar boundary layer (313). Fornearly all practically occurring gas flows, the flow regime will beturbulent in the entirety of the streaming volume, except for thelaminar boundary layer (313) covering the surface (314) wherein the flowregime is laminar. Considering a gas molecule or a particle (315) in thelaminar boundary layer (313), the velocity (316) will be substantiallyparallel to the surface (314) and equal to the velocity of the laminarboundary layer (313). Heat transport across the laminar boundary layerwill be by conduction or radiation, due to the nature of laminar flow.

Furthermore, mass transport across the laminar boundary layer will besolely by diffusion. The presence of the laminar boundary layer (313)does not provide optimal or efficient increased mass transport. Any masstransport across the boundary layer will be solely by diffusion, andtherefore often be the final limiting factor in an overall masstransport.

One impediment to the transfer or transmission of energy and/or massfrom a gas to a solid surface is the boundary layer of the gas, whichadheres to the solid surface. Even when the motion of the gas is fullyturbulent, the laminar boundary layer exists that obstructs masstransport and/or heat transfer. While various methods and types ofapparatus have been suggested for overcoming the problem such as bymeans of driving the gas with sonic waves and vibrating the solid object(100) with external vibration generators, these methods while beingeffective to some extent, are inherently limited in their ability togenerate an effective minimization of the laminar boundary layer and atthe same time covering an area large enough to make the methodefficient.

FIG. 3b schematically illustrates a flow where the effect of applyinghigh intensity and high power ultrasonic acoustic waves to/in air/gas(500) is illustrated.

More specifically. FIG. 3b illustrates the conditions when the surface(314) of a solid object (100) is applied with high intensity and highpower ultrasonic acoustic waves by a gas-jet acoustic wave generator(not shown; see e.g. 101 in other Figures) and where the high intensityand high power ultrasonic acoustic waves is absorbed in the plasma sothat the reaction is enhanced.

Again consider a gas molecule/particle (315) in the laminar layer; thevelocity (316) will be substantially parallel to the surface (314) andequal to the velocity of the laminar layer prior applying ultrasound. Inthe direction of the emitted sound field to the surface (314) in FIG. 3b, the oscillating velocity of the molecule (315) has been increasedsignificantly as indicated by arrows (317). As an example, a maximumvelocity of v=4.5 m/sec and a displacement of +/−32 μm can be achievedwhere the frequency is f=22 kHz and the sound pressure level=160 dB. Thecorresponding (vertical) displacement in FIG. 3a is substantially zerosince the molecule follows the laminar air stream along the surface. Asa result, the acoustic waves will establish a forced heat flow and/ormass transport from the surface to surrounding gas/air (500) byincreasing the conduction by minimizing the laminar boundary layer. Thesound pressure level is in one embodiment substantially 140 dB orlarger. Furthermore, the sound pressure level may be selected within therange of approximately 140-160 dB. The sound pressure level may be abovesubstantially 150 dB, above substantially 160 dB, above substantially170 dB, above substantially 180 dB, above substantially 190 dB or abovesubstantially 200 dB.

The thinning or destruction of the laminar boundary layer has the effectthat heat transfer and mass transport from the surface (314) to thesurrounding or contacting gas (500) greatly is increased, as thepresence or the reduced size of the laminar boundary layer no longerwill hind heat transfer and/or mass transport to the surface of thesolid object(s) (100) being subjected to plasma surface modification,i.e. the plasma will more efficiently influence the surface of theobject.

Furthermore, the high intensity and high power ultrasonic acoustic wavesis absorbed in the plasma so that the reaction is enhanced.

Various embodiments are described in connection with the followingfigures.

FIG. 4 schematically illustrates one embodiment of an enhanced plasmaapparatus.

Shown is at least one ultrasonic high intensity and high power acousticwave gas-jet generator (101) generating high intensity and high powerultrasonic acoustic waves (102) propagating towards and reaching aplasma (104), which will absorb the substantial acoustic energy wherebya gas-phase reaction in the plasma (104) will be enhanced due to thereceived energy.

A plasma (104) is created by a plasma source (106) using the shown gasflow, the shown electrodes (103; 103′), and an insulator or dielectricmaterial (105) e.g. as explained in connection with FIG. 1. Theparticular shown plasma source (106) is of the DBD type but could be ofanother type.

The insulator or dielectric material (105) may e.g. comprise Al₂O₃ or ingeneral material having a dielectric property or any kind of insulatorssuch as ceramics, polymers and glasses. Ceramics and glasses are moredurable against plasma since they have relatively high temperatureresistance. They are often preferred, since they typically have highdielectric constants and thus plasma can be generated and sustained atlower AC voltages.

Further shown is a hom or the like (402) or sound guiding or directingmeans that ensures that the sound intensity and power is contained andfocused towards the plasma/object.

In one embodiment, a membrane (401) or similar is located between thehigh intensity and high power ultrasonic acoustic wave generator (102)and the plasma. This enables control of the gas environment for theplasma generation process so that only the received gas flow is used increating the plasma. This may be useful for gas driven generators (102)so that the gas from such generators do not interfere with the gas mixused for plasma creation. Other embodiments may exclude the membrane(401). The membrane (401) is preferably relatively thin and relativelytransparent to ultrasound. The thickness, size, and/or shape of themembrane (401) and tension applied to it may be optimized for decreasinga loss of ultrasound.

In some embodiments, the membrane can be dispensed with even though itis not preferred that a mix of the gaseous medium used for generatingthe high intensity and high power ultrasonic acoustic waves and thegas(es) used for creating the plasma occurs. This can be achieved byhaving a high intensity and high power acoustic wave generator where thegenerated acoustic waves propagates generally in another direction thanthe general direction of the gaseous medium after exiting the acousticwave generator.

In FIG. 12 is shown two such generators where the general direction ofthe generated acoustic waves are at an angle to the general direction ofthe gaseous medium after exit from the generator.

Generators can be designed so that the two directions are aboutopposite.

For instance, stem-jet Hartmann generators radiating ultrasound in theso-called high-frequency regime allow such “natural” spatial separationof the ultrasound field and the outgoing gas flow (see e.g. Y. Y.Borisov, Acoustic gas-jet generators of Hartmann type, in L. D.Rozenberg (ed.) Sources of High-Intensity Ultrasound (New York: Plenum:1969) part I.). Such generators can be very useful in avoiding the useof a membrane as the gaseous medium may directed away from the plasma.In this way, no gas(es) used for generating the acoustic waves willinfluence the plasma gas(es). It is to be understood that even in suchan arrangement a membrane may still be useful (although it may be of adifferent design) since it can contain the gas(es) used for creating theplasma contained so they do not diffuse into the surroundingenvironment, which may be useful since some have a significant cost.

Any kinds of membranes can be used, as long as there is neithersignificant loss of ultrasound nor significant gas leakage. As long asthey can form thin films, their materials can be chosen from anythermoplastic and thermoset polymers such as polyesters, polyethyleneterephthalate, polyolefins (low density (LD) polyethylene (PE), highdensity (HD) PE, ultrahigh density PE, ultrahigh molecular weight PE,polypropylene, poly(vinyl chloride), poly (vinylidene chloride),polystyrene, polyimide, polyamide, poly (vinyl vinyl ether),polyisobutylene, polycarbonate, polystyrene, polyurethane, poly (vinylacetate), poly-acrylonitrile, natural and synthetic rubbers, polymeralloys, copolymers, and their laminates. They can be coated with organicand/or inorganic materials using any existing techniques. Among them,lower density materials such as PE can be used. Furthermore, a metalfoil may be used as a membrane. Other examples are metal coated (ormaterial coated with inorganic material) or laminated polymer membranes.

As an alternative, the membrane may comprise or consist of Aerogel.

In one embodiment, the electrode located between the plasma (104) andthe generator (101) is a mesh type of electrode (103′) or another typeof perforated electrode. This enables the generated ultrasound tovirtually pass unhindered to the object(s) (100) without loosing asignificant amount of energy whereby as much energy as possible ispresent for influencing the laminar sub-layer around the object(s)(100). Other embodiments may exclude the mesh type/perforated electrode(103′).

The direction of outgoing gas/gas mixture, used for creating the plasma(104), and the ultrasound (102) is quite controllable and the anglebetween their principal directions may vary. In the shown embodiment,the angle is about 90°. But the angle may in principal be any angle. InFIG. 5 for example, the angle is about 0°.

The gas or gas mixture used for creating the plasma (104) may also beused for driving the gas-jet acoustic generator(s) (101). The plasma(104) may be generated before, in or after the acoustic generator (101).

FIG. 5 schematically illustrates an alternative embodiment of anenhanced plasma apparatus. This embodiment corresponds to the embodimentshown and explained in connection with FIG. 4 except that the gas forthe plasma is not fed from the side but rather from the same directionas the high intensity and high power ultrasonic acoustic waves (102).

FIG. 6 schematically illustrates an alternative embodiment of anenhanced plasma apparatus. This embodiment corresponds to the embodimentshown and explained in connection with FIG. 4 except that it does notcomprise a membrane. Such an embodiment is suitable for ambient ornormal air plasma. In such an embodiment without a membrane, a highspeed air flow used for the generation of high intensity and high powerultrasound can also be used as a process gas for the plasma.

FIG. 7 schematically illustrates an embodiment of an enhanced plasmaapparatus where the plasma source is a surface discharge (SD) plasmasource. The shown embodiment corresponds to the embodiment shown andexplained in connection with FIG. 4 except that instead of a DBD plasmasource it comprises a surface discharge (SD) plasma source (106)comprising a single insulator or dielectric material (105) and a numberof electrodes (103) embedded in the insulator or the dielectric material(105). The shown SD plasma source is the so-called comprises a so-calledCDSD discharge element. Alternatively, it could comprise a SPCPdischarge element or by of another type of SD plasma source. As analternative to the gas flow being received from the side, it could besupplied in the direction of the ultrasonic high intensity and highpower acoustic waves e.g. as shown in FIG. 5 or in another way.

FIG. 8 schematically illustrates an embodiment of an enhanced plasmaapparatus where the plasma source is a torch plasma source e.g. agliding arc plasma source. The shown embodiment corresponds to theembodiment shown and explained in connection with FIG. 4 except thatinstead of a DBD plasma source it comprises a torch plasma source e.g. agliding arc plasma source.

The torch plasma source could e.g. be a barrier torch design or coldplasma torch design as well-known in the art.

FIG. 9 schematically illustrates an embodiment of a high intensity andhigh power acoustic wave gas-jet generator in the form of a disk-shapeddisk jet (i.e. a disk-jet Hartmann ultrasound generator). Shown is anembodiment of a high intensity ultrasound generator (101), in thisexample a so-called disk-jet. The generator (101) comprises a generallyannular outer part (305) and a generally cylindrical inner part (306),in which an annular cavity (304) is recessed. Through an annular gaspassage (303) gases may be diffused to the annular opening (302) fromwhich it may be conveyed to the cavity (304). The outer part (305) maybe adjustable in relation to the inner part (306), e.g. by providing athread or another adjusting device (not shown) in the bottom of theouter part (305), which further may comprise fastening means (not shown)for locking the outer part (305) in relation to the inner part (306),when the desired interval there between has been obtained. Such anultrasound device may generate a frequency of about 22 kHz at a gaspressure of 4 atmospheres. The molecules of the gas are thus able tomigrate up to 33 μm about 22,000 times per second at a velocity of 4.5m/s. These values are merely included to give an idea of the size andproportions of the ultrasound device and by no means limit of the shownembodiment.

FIG. 10 is a sectional view along the diameter of the high intensity andhigh power acoustic wave generator (101) in FIG. 9 illustrating theshape of an opening (302), a gas passage (303) and a cavity (304) moreclearly. As mentioned in connection with FIG. 9 the opening (302) isgenerally annular. The gas passage (303) and the opening (302) aredefined by the substantially annular outer part (305) and thesubstantially cylindrical inner part (306) arranged therein. The gas jetdischarged from the opening (302) hits the substantially circumferentialcavity (304) formed in the inner part (306), and then exits the highintensity ultrasound generator (101). As previously mentioned the outerpart (305) defines the exterior of the gas passage (303) and is furtherbeveled at an angle of about 30° along the outer surface of its innercircumference forming the opening of the high intensity ultrasoundgenerator, wherefrom the gas jet may expand when diffused. Jointly witha corresponding beveling of about 60° on the inner surface of the innercircumference, the above beveling forms an acute-angled circumferentialedge defining the opening (302) externally. The inner part (306) has abeveling of about 45° in its outer circumference facing the opening andinternally defining the opening (302). The outer part (305) may beadjusted in relation to the inner part (306), whereby the pressure ofthe gas jet hitting the cavity (304) may be adjusted. The top of theinner part (306), in which the cavity (304) is recessed, is also beveledat an angle of about 45° to allow the oscillating gas jet to expand atthe opening of the high intensity ultrasound generator.

FIG. 11 schematically illustrates another embodiment of a high intensityand high power acoustic wave generator in form of an elongated body.Shown is a high intensity and high power gas-jet acoustic wave generator(101) comprising an elongated substantially rail-shaped body, where thebody is functionally equivalent with the embodiments shown in FIGS. 9and 10. In this embodiment the outer part comprises one rail-shapedportion (305), which jointly with a rail-shaped other part (306) formsan ultrasound device (101). A gas passage (303) is provided between therail-shaped portion (305) and the rail-shaped other part (306). The gaspassage has an opening (302) conveying emitted gas from the gas passage(303) to a cavity (304) provided in the rail-shaped other part (306).One advantage of this embodiment is that a rail-shaped body is able tocoat a far larger surface area than a circular body. Another advantageof this embodiment is that the high intensity and high power acousticwave generator may be made in an extruding process, whereby the cost ofmaterials is reduced.

FIG. 12 schematically illustrates an embodiment of a high intensity andhigh power acoustic generator comprising two generators. Shown is anexample of two gas-jet high intensity and high power acoustic wavegenerators (101; 101′), a first (101) and a second (101′), where eachgenerator (101; 101′) generates high intensity and high power acousticwaves (102) using a gaseous medium (121). The gaseous medium (121) exitseach generator (101) in a principal direction schematically indicated byarrow (A; A′) in a cone-like shape, as represented by the hatched area,towards the generated plasma.

The high intensity and high power acoustic waves (102) generated by thefirst generator (101) propagate in a principal direction asschematically indicated by arrows (B) that is different than the generaldirection of the gaseous medium (A) from the first generator (101) dueto the design of the high power acoustic wave generator (101).

The high intensity and high power acoustic waves (102) generated by thesecond generator (101′) propagate in a general direction asschematically indicated by arrow (B′).

One example of a high intensity and high power acoustic wave generatoroperating in a way like this is shown and explained in connection withFIG. 11. This design generates high intensity and high power acousticwaves in a substantial line (seen from above), whereas the design ofFIGS. 9 and 10 generates waves in a substantially circular way.

The first (101) and the second high power acoustic wave generator (101)are located in relation to each other so that at least a part of thegenerated high intensity and high power acoustic waves (102) from thesecond acoustic wave generator (101′) has a general direction (B′) thatis directed towards at least a part of the gaseous medium (121) from thefirst acoustic wave generator (101) and that at least a part of thegenerated high intensity and high power acoustic waves (102) from thefirst acoustic wave generator (101) has a general direction (B) that isdirected towards at least a part of the gaseous medium (121) from thesecond acoustic wave generator (101′).

By directing high intensity and high power acoustic waves generated bythe second generator (101) directly towards the gaseous medium (121)from the first generator (101), energy is supplied in as a direct way aspossible so that it directly influences the gaseous medium (121) therebyincreasing the efficiency or turbulence of the gaseous medium.

This gives a very compact and efficient setup as the gaseous medium ofeach generator is enhanced by the high intensity and high power acousticwaves of another generator using a total of only two generators.

If only a single generator (101) was used, the difference between thegeneral directions of the high intensity and high power acoustic waves(B or B′) and the general direction of the gaseous medium (A or A′) fora single generator (101) would cause a loss in efficiency since theacoustic waves do not coincide with the gaseous medium (121).

The location of the generators (101; 101′) in relation to each other mayvary. One example is e.g. where the two generators are facing each otherdisplaced or shifted but where the high intensity and high poweracoustic waves still directly influences the gaseous medium of the othergenerator.

In the figure, the shown sizes, directions, etc. of the cones (121; 102)do not relate to any specific physical properties like acoustic waveintensity, etc. but merely serve for illustrational purposes. Theintensities and/or power of the two generators (101) may be equal ordifferent (with either one being greater than the other is).Furthermore, the shapes, sizes, and directions may vary from applicationto application.

The specific location of one of the generator (101; 101′) may also varyin relation to the other generator and may e.g. be placed above orhigher than and/or e.g. facing, the other generator (101); as long asthe acoustic waves (102) of one generator (101) directly influences thegaseous medium (121) of the other generator (101) and vice versa.

Although this particular example shows two generators it is to beunderstood that a given arrangement may comprises additional generators.

The gaseous medium (102) may in general be any gaseous medium. In oneembodiment the gaseous medium (102) is steam. In an alternativeembodiment the gaseous medium (102) comprises one or more gases used forcreating the plasma.

It is to be noted, that one or more of the acoustic generators shown inconnection with FIG. 12 or any other Figure could comprise one or morereflectors e.g. of generally parabolic or elliptical shape for directingthe acoustic energy to a preferred region or spot.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps or components but does not preclude thepresence or addition of one or more other features, integers, steps,components and/or groups thereof.

In the claims, any reference signs placed between parentheses shall notbe constructed as limiting the claim. The word “comprising” does notexclude the presence of elements or steps other than those listed in aclaim. The word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements.

The invention can be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer orprocessor. In the system and device claims enumerating several means,several of these means can be embodied by one and the same item of shardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

Additional Aspects:

A. A method of enhancing a gas-phase reaction in a plasma comprising:

-   -   creating plasma (104) by at least one plasma source (106), and

characterized in that the method further comprises:

-   -   generating ultrasonic high intensity and high power acoustic        waves (102) having a predetermined amount of acoustic energy by        at least one ultrasonic high intensity and high power gas-jet        acoustic wave generator (101), where said ultrasonic high        intensity and high power acoustic waves are directed to        propagate towards said plasma (104) so that at least a part of        said predetermined amount of acoustic energy is absorbed into        said plasma (104), and where a sound pressure level of said        generated ultrasonic high intensity and high power acoustic        waves (102) is at least substantially 140 dB and where an        acoustic power of said generated ultrasonic high intensity and        high power acoustic waves (102) is at least substantially 100 W.

B. A method according to aspect A, wherein said sound pressure level ofsaid generated ultrasonic high intensity and high power acoustic waves(102) is

-   -   at least substantially 150 dB,    -   at least substantially 160 dB,    -   at least substantially 170 dB,    -   at least substantially 180 dB,    -   at least substantially 190 dB, or    -   at least substantially 200 dB.

C. A method according to any one of aspects A-B, wherein said acousticpower of said generated ultrasonic high intensity and high poweracoustic waves (102) is

-   -   at least substantially 200 W,    -   at least substantially 300 W,    -   at least substantially 400 W,    -   about 400 W,    -   greater than substantially 400 W,    -   at least substantially 500 W,    -   at least substantially 1 kW, or    -   selected from about 1-2 kW.

D. A method according to any one of aspects A-C, wherein said plasmasource (106) comprises at least one source selected from a group of: adielectric barrier discharge (DBD) plasma source, a surface discharge(SD) plasma source, a volume discharge (VD) plasma source, a plasmatorch source, an arc plasma torch, a gliding arc plasma torch, a coldplasma torch, a pencil-like torch, a direct current plasma source, acapacitively coupled plasma source, a pulsed plasma source, a magnetronplasma source, an electron cyclotron resonance plasma source, aninductively coupled plasma source, a helicon plasma source, a helicalresonator plasma source, a microwave plasma source, an atmosphericpressure plasma jet (APPJ) source, a barrier torch, an arc microwavetorch, a corona discharge plasma source, a micro-plasma source, a lowpressure plasma source, and a high pressure plasma source.

E. A method according to any one of aspects A-D, wherein a working gaspressure at an inlet of said at least one ultrasonic high intensity andhigh power gas-jet acoustic wave generator (101) is betweenapproximately 1.9 and approximately 5 bar.

F. A method according to any one of aspects A-E, wherein said plasma(104) is created at atmospheric pressure.

G. A method according to any one of aspects A-F, wherein said plasmasource (106) comprises at least one electrode (103; 103′) and whereinone electrode (103′) of said at least one electrode (103; 103′) is amesh type of electrode.

H. A method according to any one of aspects A-G, wherein the generatedultrasonic high intensity and high power acoustic waves are propagatedtowards a membrane (401) so that any gases used by the at least oneultrasonic high intensity and high power acoustic wave generator (101)is not mixed with one or more gases (111) used by said plasma source(106) to create said plasma (104).

I. A method according to aspects A-H, wherein the generated ultrasonichigh intensity and high power acoustic waves (102) are generated using agaseous medium (121) and where the acoustic waves (102) are directedtowards said surface (314) of the object (100) and wherein said gaseousmedium (121) after exit of said at least one ultrasonic high intensityand high power gas-jet acoustic wave generator (101) is directed awayfrom said plasma (104).

J. A method according to any one of aspects A-I, wherein a gas mixture(111) used for creating the plasma (104) is supplied to at least oneelectrode (103; 103′) of the plasma source (106) substantially in adirection that said ultrasonic acoustic waves propagate towards saidplasma (104).

K. A method according to any one of aspects A-J, wherein said at leastone ultrasonic high intensity and high power gas-jet acoustic wavegenerator (101) is selected from the group of:

-   -   a Hartmann type gas-jet generator,    -   a Levavasseur type gas-jet generator,    -   a generator comprising an outer part (305) and an inner part        (306) defining a passage (303), an opening (302), and a cavity        (304) provided in the inner part (306), where said ultrasonic        high intensity and high power gas-jet acoustic wave generator        (101) is adapted to receive a pressurized gas and pass the        pressurized gas to said opening (302), from which the        pressurized gas is discharged in a jet towards the cavity (304),    -   a generator of any of the above mentioned types, which includes        any type of concentrators or reflectors of acoustic waves.

L. A method according to any one of aspects A-K, wherein a food item issubjected to the plasma (104) where the creation of the plasma (104)generates chemical radicals and sterilizes the food item.

M. A method according to any one of aspects A-L, wherein said generatingultrasonic high intensity and high power acoustic waves (102) comprises:

-   -   generating high intensity and high power acoustic waves (102) by        a first acoustic wave generator (101) using a gaseous medium        (121) where the gaseous medium (121), after exit from the first        acoustic wave generator (101), has a first principal        direction (A) that is different from a second principal        direction (B) of the high intensity and high power acoustic        waves (102) generated by the first acoustic wave generator        (101),    -   generating high intensity and high power acoustic waves (102) by        a second acoustic wave generator (101′),    -   where the first (101) and second acoustic wave generators (101′)        are located in relation to each other so that at least a part of        the generated high intensity acoustic waves (102), being        generated by said second acoustic wave generator (101′), is        directed towards at least a part of the gaseous medium (121)        after exit from said first acoustic wave generator (101).

N. A method according to any one of aspects A-M, wherein said plasma(104) is used in a process selected from the group of:

-   -   ozone generation,    -   hydrogen production,    -   exhaust gas cleaning,    -   pollution control,    -   odor removal,    -   fuel conversion,    -   sterilization, and    -   oxidation.

O. A system for enhancing a gas-phase reaction in a plasma comprising:

-   -   at least one plasma source (106) adapted to create plasma (104),        characterized in that the system further comprises:    -   at least one ultrasonic high intensity and high power gas-jet        acoustic wave generator (101) adapted to generate ultrasonic        high intensity and high power acoustic waves (102) having a        predetermined amount of acoustic energy and being directed to        propagate towards said plasma (104) so that at least a part of        said predetermined amount of acoustic energy is absorbed into        said plasma (104), and where a sound pressure level of said        generated ultrasonic high intensity and high power acoustic        waves (102) is at least substantially 140 dB and where an        acoustic power of said generated ultrasonic high intensity and        high power acoustic waves (102) is at least 100 W.

P. A system according to aspect O, wherein the sound pressure level ofsaid generated ultrasonic high intensity and high power acoustic waves(102) is

-   -   at least substantially 150 dB,    -   at least substantially 160 dB,    -   at least substantially 170 dB,    -   at least substantially 180 dB,    -   at least substantially 190 dB, or    -   at least substantially 200 dB.

Q. A system according to any one of aspects O-P, wherein said acousticpower of said generated ultrasonic high intensity and high poweracoustic waves (102) is

-   -   at least substantially 200 W,    -   at least substantially 300 W,    -   at least substantially 400 W,    -   about 400 W,    -   greater than substantially 400 W,    -   at least substantially 500 W,    -   at least substantially 1 kW, or    -   selected from about 1-2 kW.

R. A system according to any one of aspects O-Q, wherein said plasmasource (106) comprises at least one source selected from a group of: adielectric barrier discharge (DBD) plasma source, a surface discharge(SD) plasma source, a volume discharge (VD) plasma source, a plasmatorch source, an arc plasma torch, a gliding arc plasma torch, a coldplasma torch, a pencil-like torch, a direct current plasma source, acapacitively coupled plasma source, a pulsed plasma source, a magnetronplasma source, an electron cyclotron resonance plasma source, aninductively coupled plasma source, a helicon plasma source, a helicalresonator plasma source, a microwave plasma source, an atmosphericpressure plasma jet (APPJ) source, a barrier torch, an arc microwavetorch, a corona discharge plasma source, a micro-plasma source, a lowpressure plasma source, and a high pressure plasma source.

S. A system according to any one of aspects O-R, wherein a working gaspressure at an inlet of said at least one ultrasonic high intensity andhigh power gas-jet acoustic wave generator (101) is betweenapproximately 1.9 and approximately 5 bar.

T. A system according to any one of aspects O-S, wherein said plasma(104) is created at atmospheric pressure.

U. A system according to any one of aspects O-T, wherein said plasmasource (106) comprises at least one electrode (103; 103′) and whereinone electrode (103′) of said at least one electrode (103; 103′) is amesh type of electrode.

V. A system according to any one of aspects O-U, wherein said systemfurther comprises a membrane (401) and where the system is adapted topropagate the generated ultrasonic high intensity and high poweracoustic waves towards the membrane (401) so that any gases used by theat least one ultrasonic high intensity and high power acoustic wavegenerator (101) is not mixed with one or more gases (111) used by saidplasma source (106) to create said plasma (104).

W. A system according to any one of aspects O-V, wherein the generatedultrasonic high intensity and high power acoustic waves (102) aregenerated using a gaseous medium (121) and where the acoustic waves(102) are directed towards said plasma (104) and wherein said gaseousmedium (121) after exit of said at least one ultrasonic high intensityand high power gas-jet acoustic wave generator (101) is directed awayfrom said plasma (104).

X. A system according to any one of aspects O-W, said plasma source(106) comprises at least one electrode (103; 103′) and wherein a gasmixture (111) used for creating the plasma (104) is supplied to the atleast one electrode (103; 103′) substantially in a direction that saidultrasonic acoustic waves propagates towards said plasma (104).

Y. A system according to any one of aspects O-X, wherein said at leastone ultrasonic high intensity and high power gas-jet acoustic wavegenerator (101) is selected from the group of:

-   -   a Hartmann type gas-jet generator,    -   a Levavasseur type gas-jet generator,    -   a generator comprising an outer part (305) and an inner part        (306) defining a passage (303), an opening (302), and a cavity        (304) provided in the inner part (306), where said ultrasonic        high intensity and high power gas-jet acoustic wave generator        (101) is adapted to receive a pressurized gas and pass the        pressurized gas to said opening (302), from which the        pressurized gas is discharged in a jet towards the cavity (304),    -   a generator of any of the above mentioned types, which includes        any type of concentrators or reflectors of acoustic waves.

Z. A system according to any one of aspects O-Y, wherein a food item issubjected to the plasma (104) where the creation of the plasma (104)generates chemical radicals and sterilizes the food item.

AA. A system according to any one of aspects O-Z, wherein said at leastone ultrasonic high intensity and high power gas-jet acoustic wavegenerator (101) comprises

-   -   a first acoustic wave generator (101) for generating high        intensity acoustic waves (102) using a gaseous medium (101)        where the gaseous medium (101) after exit from said first        acoustic wave generator (101) has a first principal        direction (A) that is different from a second principal        direction (8) of generated high intensity acoustic waves (102)        being generated by said first acoustic wave generator (101), and    -   at least a second acoustic wave generator (101′) for generating        high intensity acoustic waves (102), where said first (101) and        second acoustic wave generators (101′) are located in relation        to each other so that at least a part of the generated high        intensity acoustic waves (102), being generated by one of said        first (101) and second (101′) acoustic wave generator, is        directed towards at least a part of the gaseous medium (101)        after exit from the other of said first (101) and said second        (101′) acoustic wave generator.

BB. A system according to any one of aspects O-AA, wherein said plasma(104) is used in a process selected from the group of:

-   -   ozone generation,    -   hydrogen production,    -   exhaust gas cleaning,    -   pollution control,    -   odor removal,    -   fuel conversion,    -   sterilization, and    -   oxidation.

1. (canceled) 2: A system for enhancing a gas-phase reaction in a plasmacomprising: at least one plasma source adapted to create plasma, atleast one ultrasonic high intensity and high power acoustic wavegenerator adapted to generate ultrasonic high intensity and high poweracoustic waves having a predetermined amount of acoustic energy andbeing directed to propagate towards said plasma so that at least a partof said predetermined amount of acoustic energy is absorbed into saidplasma, and where an acoustic power of said generated ultrasonic highintensity and high power acoustic waves is at least 100 W; wherein theacoustic wave generator is a gas-jet acoustic wave generator, wherein asound pressure level of said generated ultrasonic high intensity andhigh power acoustic waves is at least substantially 140 dB; and whereinthe system comprises further comprises a membrane, wherein the system isadapted to propagate the generated ultrasonic high intensity and highpower acoustic waves towards the membrane so that any gases used by theat least one ultrasonic high intensity and high power acoustic wavegenerator is not mixed with one or more gases used by said plasma sourceto create said plasma. 3: A system according to claim 2, wherein themembrane is a thermoplastic or thermoset polymer. 4: A system accordingto claim 2, wherein the membrane is made from a material selected fromthe group of: polyesters, polyethylene terephthalate, polyolefins, lowdensity polyethylene, high density polyethylene, ultrahigh densitypolyethylene, ultrahigh molecular weight polyethylene, polypropylene,poly vinyl chloride, poly vinylidene chloride, polystyrene, polyimide,polyamide, poly vinyl ether, polyisobutylene, polycarbonate,polystyrene, polyurethane, poly vinyl acetate, poly-acrylonitrile,natural and synthetic rubbers, polymer alloys, copolymers, and theirlaminates. 5: A system according to claim 3, wherein the membrane iscoated with one or both of organic and inorganic materials. 6: A systemaccording to claim 2, wherein the membrane is a metal foil. 7: A systemaccording to claim 2, wherein the membrane is metal coated or alaminated polymer membrane. 8: A system according to claim 2, whereinthe membrane comprises or consists of Aerogel. 9: A system according toclaim 2, wherein the sound pressure level of said generated ultrasonichigh intensity and high power acoustic waves is at least substantially150 dB, at least substantially 160 dB, at least substantially 170 dB, atleast substantially 180 dB, at least substantially 190 dB, or at leastsubstantially 200 dB. 10: A system according to claim 2, wherein saidacoustic power of said generated ultrasonic high intensity and highpower acoustic waves is at least substantially 200 W, at leastsubstantially 300 W, at least substantially 400 W, about 400 W, greaterthan substantially 400 W, at least substantially 500 W, at leastsubstantially 1 kW, or selected from about 1-2 kW. 11: A systemaccording to claim 2, wherein said plasma source comprises at least onesource selected from a group of: a dielectric barrier discharge plasmasource, a surface discharge plasma source, a volume discharge plasmasource, a plasma torch source, an arc plasma torch, a gliding arc plasmatorch, a cold plasma torch, a pencil-like torch, a direct current plasmasource, a capacitively coupled plasma source, a pulsed plasma source, amagnetron plasma source, an electron cyclotron resonance plasma source,an inductively coupled plasma source, a helicon plasma source, a helicalresonator plasma source, a microwave plasma source, an atmosphericpressure plasma jet source, a barrier torch, an arc microwave torch, acorona discharge plasma source, a micro-plasma source, a low pressureplasma source, and a high pressure plasma source. 12: A system accordingto claim 2, wherein a working gas pressure at an inlet of said at leastone ultrasonic high intensity and high power gas-jet acoustic wavegenerator is between approximately 1.9 and approximately 5 bar. 13: Asystem according to claim 2, wherein said plasma is created atatmospheric pressure. 14: A system according to claim 2, wherein saidplasma source comprises at least one electrode and wherein one electrodeof said at least one electrode is a mesh type of electrode. 15: A systemaccording to claim 2, wherein the generated ultrasonic high intensityand high power acoustic waves are generated using a gaseous medium andwhere the acoustic waves are directed towards said plasma and whereinsaid gaseous medium after exit of said at least one ultrasonic highintensity and high power gas-jet acoustic wave generator is directedaway from said plasma. 16: A system according to claim 2, said plasmasource comprises at least one electrode and wherein a gas mixture usedfor creating the plasma is supplied to the at least one electrodesubstantially in a direction that said ultrasonic acoustic wavespropagates towards said plasma. 17: A system according to claim 2,wherein said at least one ultrasonic high intensity and high powergas-jet acoustic wave generator is selected from the group of: aHartmann type gas-jet generator, a Levavasseur type gas-jet generator, agenerator comprising an outer part and an inner part defining a passage,an opening, and a cavity provided in the inner part, where saidultrasonic high intensity and high power gas-jet acoustic wave generatoris adapted to receive a pressurized gas and pass the pressurized gas tosaid opening, from which the pressurized gas is discharged in a jettowards the cavity, a generator of any of the above mentioned types,which includes any type of concentrators or reflectors of acousticwaves. 18: A system according to claim 2, wherein a food item issubjected to the plasma where the creation of the plasma generateschemical radicals and sterilizes the food item. 19: A system accordingto claim 2, wherein said at least one ultrasonic high intensity and highpower gas-jet acoustic wave generator comprises a first acoustic wavegenerator for generating high intensity acoustic waves using a gaseousmedium where the gaseous medium after exit from said first acoustic wavegenerator has a first principal direction that is different from asecond principal direction of generated high intensity acoustic wavesbeing generated by said first acoustic wave generator, and at least asecond acoustic wave generator for generating high intensity acousticwaves, where said first and second acoustic wave generators are locatedin relation to each other so that at least a part of the generated highintensity acoustic waves, being generated by one of said first andsecond acoustic wave generator, is directed towards at least a part ofthe gaseous medium after exit from the other of said first and saidsecond acoustic wave generator. 20: A system according to claim 2,wherein said plasma is used in a process selected from the group of:ozone generation, hydrogen production, exhaust gas cleaning, pollutioncontrol, odor removal, fuel conversion, sterilization, and oxidation.